m-PEG6-(CH2)6-Phosphonic acid

m-PEG6-(CH2)6-Phosphonic acid is a PEG-derived, phosphonic-acid-containing building block comprising a methoxy-terminated oligoethylene glycol segment, an extended linear alkyl spacer, and a terminal phosphonic acid group. The polyether and hydrocarbon regions provide a flexible scaffold with both polar and nonpolar characteristics. This compound may be used in PROTAC-related or other conjugate synthesis when a long PEG–alkyl spacer and a terminal phosphorus-containing functionality are required.

Structure: The molecule contains a methoxy-terminated PEG chain connected through a saturated linear alkyl spacer to a terminal phosphonic acid group. It does not contain an aromatic ring. The ether oxygen atoms provide hydrogen-bond-accepting sites, while the phosphonic acid group can participate in hydrogen bonding and undergo pH-dependent ionization. The C–C and C–O single-bond-rich backbone remains conformationally flexible.

Reactivity: The phosphonic acid group can undergo acid–base neutralization to form phosphonate salts, coordinate with suitable metal ions or metal-oxide surfaces, and be converted into phosphonate esters or other derivatives under appropriately selected conditions. It should not be treated as a conventional carboxylic-acid-type amide-coupling handle. Synthetic conditions should instead be chosen according to the required phosphorus-containing connectivity, while accounting for the acidity and salt state of the phosphonic acid, water content, and the stability of other functional groups present in the coupling partners.